Conventionally, permanent magnet rotary motors including a rotor having permanent-magnet magnetic pole sections composed of permanent magnets and a stator having a stator core and exciting winding sections, have been used. As a stator core, there is known such a stator core that has an annular yoke and magnetic pole constituent member disposed inside the yoke. In the motor of this kind, the magnetic pole constituent member comprises a plurality of pole columns, magnetic pole surface constituent sections formed on the pole column and connecting portions connecting two adjacent sections among the magnetic pole surface constituent sections. Japanese Patent Publication Application No. 2000-32690 discloses a permanent magnet rotary motor in which an annular yoke and magnetic pole constituent members are arranged to fit with each other for increasing the ratio of a volume occupied by windings and facilitating fabrication thereof. Japanese Patent Publication Application No. 2002-199630 discloses a permanent magnet rotary motor in which pole columns are disposed at unequal intervals to vary the dimensions between adjacent pole columns to reduce the cogging torque. Further, Japanese Patent Publication Application No. 2002-10539 discloses a permanent magnet rotary motor in which a plurality of holes are formed discontinuously along an axial direction in its connecting portions and are opened both inwardly in a radial direction and toward a slot between two adjacent pole columns. The plurality of holes are formed in order to prevent leakage of magnetic flux among the magnetic poles.
It has been demanded for the permanent magnet rotary motor that the cogging torque should be reduced while maintaining the torque. However, the above-mentioned conventional permanent magnet rotary motors have a limitation in reducing the cogging torque.